Salt marshes occur along the upper edges of the ocean where they are periodically inundated by seawater. The salt in seawater is toxic to most plants, but plants of the saltmarsh (called halophytes) have special adaptations that allow them to desalinate the seawater to obtain fresh water for their physiological needs. Very few plant species can survive in the salt marsh. Most are low-growing and many are succulent.

In the Reserve, salt marsh is found in the lowest elevations west of Interstate 5. Most saltmarsh species are also found in the brackish marsh east of the interstate.